This invention relates generally to apparatus which mixes two liquids, and specifically to such an apparatus which mixes a viscous liquid polymer with water to provide a diluted polymer of particular use in the treatment of water.
Polymers are commonly used in water treatment equipment in order to remove solids suspended in the water. Polymers, or polyelectrolytes as they are sometimes called, carry an electrostatic charge which attracts particles suspended in water. Since virtually all solids carry a negative or positive charge, they are attracted to these polymers. Polymers are extremely large with millions of charge sites that attract suspended particles.
Polymer is available in dry or liquid form. Dry polymers are inactive because the molecules are coiled. Although being less expensive, dry polymers require complex and costly equipment to be converted into the active, liquid state. Liquid polymer may be highly concentrated, containing 15-30% active polymer, in which case the molecules are only partially uncoiled. Concentrated liquid polymer is prepared from dry polymer at chemical processing plants under exacting conditions using expensive equipment. These chemical processing plants are capable of providing the polymer at any selected concentration.
The more diluted the polymer the shorter its useful life. Dry polymer lasts indefinitely, concentrated liquid polymer lasts several months, and dilute polymer of a concentration of a few percent deteriorates in days. It is the last form which is most effective in water treatment because the molecules are fully uncoiled to provide a maximum number of charge sites to attract particles suspended in the water to be treated. But, polymer so diluted will lose much of its effectiveness during shipment and storage. It is, therefore, advantageous to ship concentrated polymer to the site of the water treatment apparatus and there provide mixing equipment to dilute the polymer and produce only as much diluted polymer as needed on a daily basis, for example.
But, in the diluted condition the uncoiled polymers are delicate and the chains are easily broken. Nor is dilution easily accomplished since the polymers do not mix readily with water.
Currently the concentrated polymer arrives at the treatment facility in drums and is transferred by use of gear pumps into mixing tanks containing water. Gear pumps tend to damage the concentrated polymer. In the tanks, mixers are used to mix the water and polymer. Metering pumps feed the diluted polymer to the water that is to be treated. Such systems range in price from $5,000 to $50,000. The mixers tend to create a great deal of shear causing the delicate polymer chains to be broken and clump together. The mixer is small compared to the size of the mixing tank, causing highly localized mixing action so that the product thus produced is not very uniform. Nor is it easy to control precisely the concentration in the tank to match the concentration as specified by the polymer manufacturer to provide optimum water treatment. Also, such equipment makes it difficult to produce the same concentration from batch to batch. Gear pumps do not enable adjusting the rate of flow of the concentrated polymer into the tank unless complicated and expensive variable speed drives are utilized.
Generally, conventional polymer feed systems are expensive to purchase and to operate, require frequent maintenance, and do not provide a satisfactory product.